Welding apparatus



Jan. 2l, 1964 R. s. zELLER 3,119,009

WELDING APPARATUS Original Filed July 15, 1955 l2 Sheets-Sheet l Jan. 21, 1964 R. s. zELLER WELDING APPARATUS Original Filed July 15, 1955 l2 Sheets-Sheet 2 Jan. 21, 1964 R. S. ZELLER WELDING APPARATUS Original Filed July l5, 1955 l2 Sheets-Sheet 3 cia/75 ws /7 7* Tax/VIK Jan. Z1, 1964 Original Filed July 15, 1955 R. s. ZELLER WELDING APPARATUS 12 Sheets-Sheet 4 as ,7 Trax/15% Jan. 2l, 1964 R. s. ZELLER 3,119,009

WELDING APPARATUS Original Filed July 15, 1955 l2 Sheets-Sheet 5 INVENTOR. ifa-Zar? zeiler'.

afn

/f/s /yrrarmafh/ Jan. 21, 1964 R` s. zELLER WELDING APPARATUS 12 Sheets-Sheet 6 Original Filed July 15, 1955 Jan. 21, 1964 R. s. ZELLER WELDING APPARATUS 12 Sheets-Sheet 7 Original Filed July l5, 1955 a INVENTOR. J S' Zeef' W /y/s /vfax/VKK Jan. 21, 1964 R. s. ZELLER WELDING APPARATUS 12 Sheets-Sheet 8 Original Filed July 15, 1955 NVENTOR. /gz'df S26/47er' BY MW;

wif/Z@ /y/s /77 Tar/VIK R. S. ZELLER WELDING APPARATUS Jan. 2l, 1964 l2 Sheets-Sheet 9 Original Filed July 15, 1955 UKN.

PRN wh Jan. 21, 1964 R. s. ZELLER 3,119,009

WELDING APPARATUS original Filed July 15. 1955 12 sheets-sheet 1o /ZM/ www Jan. 21, 1964 R. s. zELLER 3,119,009

WELDING APPARATUS www my Jan. 21, 1964 R. s. zELLl-:R

WELDING APPARATUS Original Filed July l5, 1955 12 Sheets-Sheet 12 H/s Ar r rop/v51.

K. wh v United States Patent O 3,119,009 WELDNG APPARATUS Richard S. Zeller, Detroit, Mich., assignor to Weltronic Company, Detroit, Mich., a corporation of Michigan @riginal application duly/15, 1955, Ser. No. 522,264, now Patent No. 3,019,329, dated lian. 3d, 1962. Divided and this application .luly 1.3, i961, Ser. No. 125,926 Claims. (Cl. 2l9-125) This invention relates t0 welding and more particularly to automatic arc welding apparatus and is a division of my application Serial No. 522,264, tiled July 15, 1955, now Patent No. 3,0\i9,329.

in general, in the disclosed preferred embodiment of the invention, welding is performed by the establishing of a high-current arc between an electrode and the work in an inert-gas shielding atmosphere. Means are provided for moving the Iwelding electrode along the work at a controlled rate, for varying the distance between the electrode and the work to establish the arc and to maintain the voltage between the arc `and the work at a substantially constant preselected value, and for feeding fusible wire to the work area at a controiled and preselected rate. A switching arrangement functions to initiate these movements, to vary, automatically, the rate of movement of the electrode along the wonk and the rate of feed of the fusible wire in accordance with a selected pattern, and to terminate the systems elemental operations at preselected appropriate times.

In the arc welding of two work edges together (as, `for example, the adjacent edges of two plate members or the adjacent edges of a single metal piece formed with two adjacent edges) it is desirable to start at one end of the juxtaposed edges and then to gradually provide relative movement between the arc and work from the said one end along the juxtaposed edges and terminate at the other end of the edges. It has previously been recognized to be desirable to initiate the arc welding at a lesser current ilow when the arc is closely adjacent the beginning end of the edges and, as the arc moves away from said one end, to rapidly upslope or increase the arc current from the initial value to a full value. Thereafter as t..e arc nears the opposite end of the edges, it is desirable to rapidly down-slope or decrease the arc current. In prior devices, however, the circuit inductances have been such that the minimum up-slope time interval has been about .25() second and the minimum down-slope time has been about .500 second. With the more rapid slope times provided by the practice of the principles of the present invention is possible to satisfactorily weld at greater welding speeds, to weld thinner materials, to weld with greater precision, and, in instances where old apparatus could weld by the use of welding tabs, to eliminate the necessity for such tabs and their inherent disadvantages.

An object of this invention is to improve the preciseness with which a welding current may be caused to vary in amplitude with time.

A feature of this invention is an improved means for moving a welding electrode in either of two directions along the work under automatic control.

Another feature of the invention is an improved means for controlling the instant at which an arc current will commence to change from one value to another value.

Another feature of this invention is an improved means for controllably varying the rate at which `fusible Wire is fed to the welding area.

Another feature of lthe invention is an improved current controlling mechanism which can change the current magnitude from a first preselected vaue to a second preselected value in a time interval of iive hundredths of a second or less.

'ice

The manner of accomplishment of the foregoingy objects, the` detailed nature of the foregoing features, and other objects and features of the invention, will be perceived from the yfollowing detailed description of an FIG. 2 is a schematic representation of a portion of thel electrical circuits for controlling the time, sequence and nature ofthe operations of the apparatus of FIG. 1;

FIG. 3 is a schematic representation of another portion ofthe electrical control circuits, and should be placed below FIG. 2. for proper orientation;

FIG. 4 is a schematic representation of another portion of the electrical control circuits, and should be placed below FIG. 3 for proper orientation;

FIG. 5 is a schematic representation of certain of the power-supply transformer windings and a portion of an apparatus for controlling the amplitude of the welding current;

FiG. 6 is a schematic representation of a further portion of the apparatus for controlling the amplitude of the welding current, and should be placed below FdG. 5 for proper orientation;

FIG. 7 is a schematic representation of a further portion ofthek welding current control apparatus and should be placed below FIG. 6 for proper orientation, and further inciudes a portion of the apparatus for controlling the length of the welding arc;

FIG. 8 is a schematic representation of the remainder of the arc length control apparatus and should be placed below FiG. 7 for proper orientation;

FIG. 9` is a schematic representation of the electrical apparatus for controlling the motionv of the carriage, an element of the apparatus of FIG. 1;

FIG. l() is a schematic representation of the lapparatus for controlling the feed of the filler wire in the welding,r operation as performed by the apparatus of FIG. l;

FIG. ll is a schematic representation of a time delay mechanism suitable for use in the time delay units represented in block schematic form in FlGS. 3 and 4 of the drawings;

FiG. 12 is an indexing reference sheet identifying the figures upon which each relay winding and its several contacts may be found; and

FiG. 13 is a chart showing the operating sequence of various of the relays and switches of the electrical apparatus.

A machine embodying certain of the mechanical and electrical aspects of the invention is represented in a generally functional form in FIG. l of the drawings. Certain of the mechanical elements are basically similar to corresponding portions of commercially available radial drills, and many of the mechanical retinementsthere employed may be utilized to advantage in the present structure.

In general, the structure comprises a base 2d rotatably supporting a vertical column 22. A ring gear 24, fixed to the column 22, is engageable by a pinion 26 capable of being driven by a reversible motor 2S, normally through appropriate reduction gearing. An arm Bti is supported upon the column 22, an appropriate keying arrangement being provided so that the arm 30 may move in translation in a vertical sense upon and with respect to the column 22 but is locked against rotation relative to the column 22. Hence, rotation of the column 22, as a result of energization of motor 28, will produce consequent rotation of the arm 3i) about the vertical, longitudinal axis of the column 22.

`It is assumed that the permissible rotation of the column 22 and -arm 3i? is slightly less than 360. As an element of the electrical apparatus hereinafter to be described, a pair of limit switches L59 and LS1@ may be rfixed with respect to the base Ztl and positioned to engage an element such as pin 32, mounted on the gear 2d, for sensing when the column 22 and arm 3d have reached their preselected limits of rotation in each direction.

Clamping means 29 may be mounted upon the base Ztl and engageable with some portion of the gear 24 or column ZZ and effective, when energized, to firmly ciamp the ring and column against rotation. A limit switch S6 is preferably provided to sense the clamped or unclamped condition of the column 22 and arm 30.

T he arm 3@ may be moved up and down upon the column 22. by suitable means functionally represented as a motor 3d, which may include reduction gearing, mounted upon the arm 3d and adapted to rotate a worm 36 threadedly engaging a nut fixed within a top cap 38 mounted upon the column 22. The elevating mechanism represented is, of course, but a rudimentary functional representation of the type of elevating mechanism which would be employed in practice.

As additional elements of the electrical apparatus hereinafter to be described, a limit switch L57 may be mounted upon the top cap 33 in a position to be engaged by the arm 3d when it approaches its upper limit position, and a limit switch LSS may be ati'ixed to, for example, the column 22 in a position to engage the arm 30 as it approaches its lower limit of motion.

A carriage 42 is slidably mounted upon ways 44 upon the arm Sil so as to be movable in translation along the length of arm 3i? by means such as a motor 46 driving, preferably through reduction gearing, a worm 48. A limit switch LSS may be appropriately and adjustably positioned upon the arm 3f) to engage a portion of the carriage 4Z when that carriage approaches its innermost, left-hand, or reverse position; a limit switch L53 may be mounted upon the arm 3@ in a position to engage a portion of the carriage 42 when that carriage approaches an adjustably selected, outermost, right-hand, or forward limit position; and a limit switch L84 may be adjustably positioned at an appropriate point, normally intermediate limit switches L83 and LSS. Limit switch L54, as will be noted hereinafter, is provided to sense when the weld is about completed, and hence is representatively shown in a position adjacent limit switch L33, it being assumed that the carriage 42 is moved from left to right during the actual welding operation.

The carriage 42 supports a vertically movable automatic head assembly. This assembly is represented, in a rudimentary form, as a worm Sti keyed so that it camiot rotate relative to the carriage 42 and driven by a nut rotated by a motor 52. Worm d carries a welding electrode EL. Hence, the selective rotation of motor 52 will move the electrode EL towards or away from the work W mounted upon a fixture 56.

A limit switch LSZ may be mounted upon the carriage 42 in a position to engage an element 58 upon the worm 5t) to sense when the automatic head assembly has reached its selected lower limit of motion, and a limit switch LS1 may be positioned to sense when the head assembly has reached its selected upper limit of motion.

The electrode EL is preferably water-cooled by flowing water through a water jacket (not shown) surrounding a portion of that electrode. Means are preferably provided for sensing the existence of water iiow to indicate that the cooling system is properly operating. This means may comprise a pressure-sensitive, bellows operated microswitch (labeled WFS in the circuits of FIG. 2) for detecting pressure differentials at the water jacket, and hence water ilow. The valve controlling the flow of water is also preferably solenoid operated as will be noted hereinafter.

It is also preferred that the welding operation be performed in an inert atmosphere to prevent oxidation of the electrodes and inclusion of atmospheric gases in the weld metal, especially nitrogen, and consequently a supply of an appropriate gas, such as helium or argon, may be connected to a nozzle positioned adjacent or coaxially with the welding electrode EL for directing that gas to the work area. The vaives controlling the flow of gas are preferably solenoid operated, as will be noted, and means in the form of a gas-pressure switch (labeled PS1 in the circuits of FIG. 3) is preferably provided for sensing the flow of gas at the nozzle.

It is also contemplated that a supply of fusible wire 62 be provided at the work area. This is functionally represented by a drum-and-driving-motor assembly 60 mounted upon the carriage 42 and feeding the wire 62 through a guide means 64 mounted upon but insulated from the electrode EL or its supporting structure. Driving motor d@ is or may be automatic in its operation as will be described hereinafter.

Considering now the electrical control system, certain of the elements represented in FIGS. 2 to ll are physically mounted upon the machine represented in FIG. l, others of the elements are preferably mounted in an auxiliary cabinet, and at least a portion of the control switches are preferably located on a control panel convenient to the welding electrode EL and hence convenient to the operator at the work area.

In the circuit diagrams of FIGS. 2 to 1l, the windings of relays are represented by a circle, a pair of contacts operated by that relay which are open or separated when the relay is unenergized and closed when the relay is energized, normally open contacts, are represented by a pair of parallel spaced-apart straight lines, and a pair of contacts which are closed or in engagement when the relay is unenergized and open or separated when the relay is energized, normally closed contacts, are represented by a pair of spaced-apart parallel lines bridged by an oblique line. To facilitate understanding of the functional operation of the system, the contacts are shown separated from the relay windings and in their functional relationship to other elements of the system. However, each contact is identified with a reference character identical to that of the winding of the relay of which it is a part, followed by a further distinguishing letter. Transformer windings are represented in the normal fashion except that the primary and secondary windings of certain of the transformers are separated for clarity of presentation. However, they are similarly designated so that each secondary winding may be correlated with the appropriate primary Winding. Resistors are represented by a rectangle, capacitors by spaced-apart straight and curved lines. This symbolism is conventional in the art to which this invention pertains. The remaining elements of the system are represented in a form common to most fields of the electrical art.

In the description of the circuits, when notation is made of the number of the gure in which an element is depicted, the elements subsequently discussed will be found in the same figure until attention is directed to a different figure of the drawings.

The system is intended to operate from a supply of three-phase alternating voltage of, for example, 440 volts amplitude, applied across lines Lia, L2a and L35: (FIG. 5 Upon the closure of line switch 99, one phase of this voltage, phase B appearing etween conductors L2 and L3 (FIG. 5), is applied across the primary winding of transformed STP to develop across the associated secondary winding 3T3 (FIG. 2) a single-phase alternating voltage of an appropriate amplitude, such as volts. This secondary voltage is applied, through fuses HF and tif/2F, between conductors lill and lib which extend from FiG. 2 to FIG. 4 of the drawings. Lamp EPL (FIG. 2), is connected between conductors Iii?. and iti to indicate that the power is on.

In order to establish a slight time delay between the closing of' power through `the line and the Icomplete op erationof the system, to permit filament heating and purging of the gas lines, time delay relay TD is operated over a path including normally and now closed contact TDCRQ and conductors IdZ and 104. After a selected interval, relayTD will close kits contacts TDC:y to operate relay TDCR. Relay TDCR, in operating, completes a circuit for maintaining itself energizedy which may be traced from conductor IIIZ, contact TDCRb, winding of relay TDCR and conductor N4. This circuit bypasses Contact TDa which completed Athe energizing circuit for relay TDCR. This operation of a relay in which it completes a circuit through one of its own contacts to main# tain a self-energizing circuit shunting the original energizing contact will hereinafter be referred to as sealing in, in accordance with the nomenclature customary in the art.

Relay TDCR, in operating, also opens its contact TDCRrz to release time delay relay TD, and completes a circuit from conductor 102, contacts TDCRC lamp ZPL to conductor Ill-4l to establish a visible indication that the time delay is over.

The closure of-contact TDCRC places the further functioning of the equipment under the control of the master start switch IFB. When switch IPB is momentarily depressed, relay ACR is operated, and that relay seals over a circuit including its contact ACRa andthe emergency stop switch ZPB. As will be seen, emergency stop-switch ZPB' will serve, when momentarily depressed, to terminate the motion and functioning of all elements of the machine. Lamp SPL, energized concurrently with relay ACR and maintained energized over a circuit including contact ACRa, provides avisible indication that the master start switch IPB has been operated.

The closure of contact ACRQ also connects conductor Ill?) to conductor 1416, which extends through FIGS. 2 to 4 ot the drawings, to enable the operation of the equipment connected between conductor Idd and conductor M94. Thus, the carriage motor 46 (FIG. 1) may be manually controlled, via switch Itl (FIG. 3) in a manner to be described, to move the carriage 42 (FIG. I) and the electrode EL along the arm 3@ relative to the work W. Further, the wire 62 may be manually fed to or retracted from the work W via switch II@ (FIG. 3), and the electrode EL (FIG. I) may be raised or lowered under manual control Via switch AI-ICS (FIG. 3), both in a manner to be described.

Additionally, the application of voltage between conductors Idd and Ihr, permits the arm 3l) (FIG. 1) to be moved up or down upon the column 22, permits the arm .'itlto'be rotated about the longitudinal axis of the column 22, and permits the clamping mechanism`29 to Ibe selectively energized or cie-energized. Thus, if the swinger of the arm hoist control switch III (FIG. 4) is moved into engagement with its upper contact, the voltage on conductor Ifile is applied through limit switch LS7, throughv normally and now closed contact DRIa, winding ofthe up-con'trol relay URI and through overload switches OLI and CL2 (associated with motor 34 (FIG. 5)) to conductor 11614 whereby relay URI is operated. Relay URI in operating, eilects the closure of the contacter elements Cla (FIG. 5) to so apply the power on conductors LI, LZ and L3 that the arm hoist motor 34 is caused to rotate in a proper direction to produce upward movement of the arm'3tl (FIG. I). This motion may be continued until limit switch L87 (FIGS. I and 4) is tripped.

If the swinger of switch IIZ (FIG. 4) is moved into engagement with its lower contact, the arm-down relay DRI will be energized to effect the closure of the contactor elements CII) (FIG. 5) to cause the arm hoist motor 34 to rotate in a reverse direction. Limit switch L58 (FIGS. l'and 4) establishes a lower limit to this downward motion.` Itwill be noted that a normally closed Contact URIn of the up relay URI is included in the energizing circuit for the down relay DRI, and conversely, to

protect against short circuiting of the power supply lines.

Assuming the clamping mechanism is unclampedk so that limit switch L86 (FIGS. l and 4) is closed, the-wiper of switch Il l (FIG. 4) may be moved vto its :upper `position to complete an energizing circuit for relay RRI through normally closed limit switch L59, through nor-` mally and now closed contact LRIa, and through yoverload switches @L3 and CL4, which are responsive to the condition of the arm rotate motor 2S (FIGS. 1 and 5). Relay RRI, in operating, effects lthe yclosure of the contacter elements CZa (FIG. 5) to energize the armrotate motor 23. Limit switch L89 serves to terminate the rotation of the arm in one direction when a preselected limit position is reached. Similarly, if the swinger of switch M4 is placed in engagement with its lower contact, relay LRI is energized to effect the closure of the contacter elements C2b to cause the motor 2S to rotate in the other direction, the limit of that motion being .established by the position of limit switch LSIO.

Assuming that the column clampv mechanism Z9 (FIG. I) is either motor-driven, or is an electric-motor powered hydraulic system, so that motor 29 (FIG. 5) controls the clamping operation, the column and arm may be clamped-y against movement by causing the column clamp motor 29 (FIG. 5) to rotate in one direction by moving the swinger of switch Ille (FIG. 4) to its upperposition to operate relay CLI. other direction to control the release of clamping, unclamping, when the unclamp relay ULI (FIG. 4) is energized by moving theswinger of switch II6 into engagement with its lower contact.

Thus, at this point in the systems operation, the weld-A ing electrode EL may be moved to any selected position relative to the work by the selective operation of a plurality of control switches.

T z'me Delay Circuits Certain of the operations of the equipment hereinafter' to be described are controlled by the time delay units, represented in block schematic form, TDA (FIG. 3), TDR, TDC (FIG. 4), TDD, and TDF. Each of these timers is connected between conductors III?. and 104, as their source of power, and additionally each of the timers is provided with a start leadior initiating its timing operation. Thus, timers TDA and TDB (FIG. 3) share a start lead SLab, timer TDC is provided with a start lead SLC (FIG. 4) and timers TDD and TDE share a start lead SLde. As will be noted, the control circuits function selectively to connect, at a selected time, these start leads to conductor Ill to initiate the individual timing operations.

While any appropriate time delay mechanismv may be used, a suitable .type of such mechanism is disclosed in FIG. 1I of the drawings in order that the disclosure may' be complete. In that representation, the conductors labeled IGZ and IM are identical to conductors A102 and 194 in FIGS. 2 to 4. Thefother input to the timer is a start lead labeled SL which finds its counterpart in the several enumerated start leads in FIGS. 3 and 4.

When alternating voltage is applied between conductors ItlZ and IM, as previously described, resistors 7RA and @RA serve as a voltage divider. The resultant alternating voltage across resistor GRA is applied across a circuit including capacitor ICA, which is connected'in parallel with variable resistor 1PA and xed resistor IRA, and further including fixed resistor SRA, the grid-to-cathode path of thyratron IVA, and resistor 5RA.y As a con` sequence, rectification will occur and capacitor ICA will become charged, with its left-handelectrode being positive relative to its right-hand electrode. With thecontacts ICRC: open the anode-cathode circuit of tube IVA is open and it consequently will not conduct.

This condition continues until such time as either the pilot switch PIA is depressed for some reason, or, nor- Motor 29 (FIG. 5) is rotated in theL mally, until start lead SL is connected to conductor 102 in the manner hereinafter to be described. When that connection occurs, control relay 1CR is operated to close its contact lCRcz to connect the cathode of tube 1`VA to conductor 102. The anode of tube 1VA is connected to conductor 14M through the winding of relay ZCR, which is shunted by resistor 1l-RA. The completion of the anodecathode circuit of thyratron llVA does not result in the immediate conduction of tube 1VA since closing of the contacts 1CRa `also connects the positively charged terminal of the capacitor 1CA to the cathode of thyratron 1VA and the magnitude ot the charge on this capacitor is suiicient to place a negative bias on the grid of thyratron IVA. However, when contact 1CRa closes to connect the cathode or" tube 1VA directly to conductor 102, no further rectication occurs land capacitor 1CA cornmences to discharge through resistor llRA and variable resistor 1PA, the time constant of the circuit, and hence the time delay produced by the device, being selected by adjustment of the position of variable resistor 1PA and/ or adjustment of the value of capacitor 1CA. The resistor 7RA is connected in the grid bias circuit and provides a small A.C. bias on the D.C. bias for rendering the time delay more accurate and the fixing of the thyratrons more positive. After the selected time delay, the direct-voltage bias will become reduced to the point where tube 1VA will conduct and operate relay ZCR. Thereafter, relay ZCR will be held operated as long as voltage is applied between conductors 102 `and 104.

Relay ICR is or may be provided with contacts additional to the contact 1CRa shown in FlG. ll and relay ZCR is provided with operating contacts. To avoid confusion, those contacts of `the relay ICR in the delay unit TDA (FIG. 3) are labeled lCRA followed by a lower-case distinguishing letter, those contacts of the relay ZCR which is a part or timer TDA are labeled ZCRA followed by a lower-case distinguishing letter, the contacts of the relay lCR which is a part of timer TDB are labeled lCRB followed by a lower-case distinguishing letter, and so on.

Preparation for Welding When power is rst applied between conductors 192 and 104, current flows through the normally and now closed contact TDR1a (FIG. 3) and through, in parallel, gas solenoid GSH in the automatic head, gas solenoid GSL in the gas line, and water solenoid WS, thereby turning on both the supply of gas and water. Further, at the application of power between conductors 102 and 104, a voltage is applied across a circuit including the normally and now closed contacts CR1c (FlG. 2), the gas purge switch SW4 (assuming that switch to be closed), and the winding of timer TDR1. After a selected time interval, the time delay relay or timer TDR1 opens its normally closed contact TDRlla (FIG. 3) to de-energize the gas solenoids GSH and GSL and the water solenoid WS. This operation serves primarily to purge the lines of air.

Welding The apparatus is now in condition for welding to proceed, assuming the parts to be welded are in position, that the arm 30 has been positioned, that the several controls have been appropriately manipulated to bring the welding electrode into its proper starting position, and that the column and arm have been clamped in position.

The welding operation may be performed on a fully automatic basis. When the operation of the apparatus is initiated, the flow of gas and water is started, the manual control over the motion of the elements is disabled, the welding electrode is automatically positioned, and varied in position if necessary, relative to the work to main-tain a constant arc voltage, the movement of the carriage is initiated, controlled and varied in a preselected fashion, the welding current is maintained constant or varied in a preselected manner, the feeding of the fusible wire to S the work is initiated and controlled, and each of the systems elemental operations is terminated at the appropriate time.

To commence welding, the start weld switch SFB (FIG. 2) is momentarily operated to complete a circuit from conductor M2, contact ACRa, switch BPB, contact ZCREa, winding of relay BCR to conductor 104. Relay BCR operates and seals in over a circuit including its contact BCRa and contact ACRfz. Relay BCR, in operating, also closes its contact BCRb to connect conductor 162 to conductor 121i through Contact ACRa.

Since contact TDRZa is at this time closed, the application of a voltage between conductors and 164 will result in the immediate operation of relays CRl and CRZ. Relay CR1, in operating, opens its Contact CRllc to release timer TDRll. Upon the de-energization of timer TDR1, lits contact TDRla (FIG. 3) again closes to reenergize the gas solenoids GSH and GSL and the water solenoid WS.

While this operation theoretically turns on both the gas and water, means are provided for insuring that both are being supplied as a condition precedent to further operation of the equipment. Thus, timer TDRZ (FIG. 2) is energized concurrently with the operation of relays CRll and CR2 over a circuit including the normally closed contact WFSa, which is a contact of the water-pressure-differential sensing switch WFS hereinbefore mentioned. If water does not ilow through the cooling jacket, contact WFSa remains closed, timer TDR2 operates after a selected time interval, and its contact TDRZa opens to release relays CRl and CR?. -to prevent further functioning of the equipment until the condition is corrected.

lf however, water does ilow, the water pressure differential switch WFS opens its contact WFSa to cle-energize timer TDRZ and closes its contact WFSb to energize lamp LEPL, to connote that the water is in fact flowing. Since timer TDRZ is de-energized prior to the eX- piration of its time delay interval, its contact TDRZa does not open and relays CR1 and CRZ remain operated.

If the energization of gas solenoids GSH and GSL (FIG. 3) does result in the ilow of gas, pressure switch PS1 (FIG. 3) is closed. Since contact TDRlla is now closed, relay 11CR and the gas-on lamp SPL are both energized. The closure of contact 11CRa (FIG. 2) completes a circuit including contact CR1a, contact 2CREC and the magnetic contactor WPC. As a result, contacts WPCa (FIG. 7) in lines L1, L2 and L3 are closed to initiate welding.

Arc Length Control As a result of the closure of contacts WPCa (FIG. 7), a voltage is established between the electrode EL and the work W by equipment hereinafter to be described. The voltage between electrode EL and work W also appears across the winding of relay CRS, since contact CRle is now operated. Relay CRS is a voltage sensitive relay and has a minimum Voltage for operating which is substantially greater than any operating arc voltage or drop. Since it is assumed that no arc is yet struck, relay CRS operates.

Relay CRS, in operating, closes its contact CRb (FIG. 2) to complete a circuit including now closed contact SCRa, variable resistor 21P, and the primary transformer winding 29TP. As a result, the spark gap oscillator SGO (FIG. 7) is energized to produce, through transformer 39T, a high-frequency field between the electrode EL and the work W to assist in ionization. it will be noted that if high-frequency arc starting is employed, as is here assumed, the automatic head arc starter AI-IAS (FlG. 2) is disabled by opening switch SAS, The network 33C, 39C, 3912., and WR provides a filtering network to prevent the high frequency from appearing at power supply sections.

The closure of contact CRS!) also produces the operation of relay CR (FlG. 2) which performs certain control functions in'the operation of the circuits shown in FIGS. 7 and 8 of the drawings, as will be described.

When relay CRI operated, it also closed its contact CRM (FIG. 3) to operate the automatic head raisecontrol relay CR'. Further, assuming that the automatic head is not now at its lower limit position, normally open limit switch LSZ (FIGS. l and 3) is open and relay CRE; is de-energized. Relay CRZ is energized concurrently with relay CRI and closure of its contacts CRZa energizes the automatic head lower-control relay CRIS (FIG. 3). Since timer contacts ZCRCC (FIG. 3) are at this time closed, since contact CRSb is now closed, and since contact CRla is closed due to the operation of relay CR?, the voltage between conductors 12 and 1M is applied across capacitorCIZ and one of the automatic head motor field windings AHMFA (FIG. 3). Contacts ZCRCC are utilized to prevent the motor 52 from moving the electrode during current decay or slope down. Contacts CRS!) open when limit switch LSZ is closed to prevent movement of the electrode EL toward the fixture 5d closer than a selected minimum distance. Capacitor `CIZ is utilized for phase shifting purposes. This energization of the winding AI-IMFA, plus additional functions performed as a result of the operation of relays CR6 and CR7, serves to initiate the functioning of the circuits represented in FIGS. 7 and S of the drawings.

The circuits represented on FIG. 8 and the lower portion of FIG. 7 of the drawings are generally conventional in nature and will be described in a somewhat general fashion, but the details are shown to ensure a complete understanding of the total systems operation.

The function of the dual section tube V3 (FIG. 8) is to compare the amplitude of the voltage between the electrode EL (FIG. 7) and the work W with a fixed reference voltage. The reference voltage is obtained by full-wave rectification, by tube VI (FIG. 7), of the alternating voltage appearing across the secondary winding TISZ. The resultant direct voltage appearing between conductors Mu and 141 is filtered by means including choke Xl (FIG. 8) and capacitor CI and C2, and is applied between conductors Mtl and 142 and across resistor RI and voltage regulating diode V2. The constant-amplitude voltage across diode V2 is applied across a voltage divider comprising resistor R2 and potentiometer PTI, the total voltage across potentiometer P1 being applied through resistor R4 to the control grid of the left-hand section of tube V3.

The cathodes of both sections of tube V3 are connected to the return lead Idil through a self-biasing resistor R7, and the anodes are connected through individual load resistors R5 and R6 to the positive-potential conductor MZ. Thedegree of conduction through the left-hand section of tube V3, and the potential at the anode thereof, are therefore relatively fixed at preselected values.

The arc voltage appearing between electrode EL (FIG. 7) and the work W is filtered by the choke-input filter shown in FIGS. 7 and 8 and applied across the parallel combination of capacitor C2@ (FIG. 8) and resistor R3. Resistor R3 may therefore be considered as a voltage source in the input circuit of the right-hand section of tube V3, being connected in series with that portion of the potentiometer PI between the moving element thereof and conductor ll/it). As a consequence, the conductivity, and hence the voltage at the anode, of tube V3 will be determined both by the arc voltage and the setting of potentiometer PI. If the actual arc voltage is equal to the desired arc voltage as established by the setting of potentiometer PI, the potentials at the two anodes of tube V3 will be equal. If the actual arc voltage is greater than the selected and desired arc voltage, the right-hand section of tube V3 will conduct more current than the left-hand section so that the anode of the right-hand section will be at a lower potential than that of the left-hand section, and conversely.

The signals at the anodes of tube V3 are coupled to and amplified by the two sections, respectively, of tube V4, potentiometers P2 being provided to vary the zerosignal bias on the two sections of tube V4 and hence to act as a sensitivity control.

Since relay CRZ (FIG. 2) is operated as previously escribed, contacts CRZe (FIG. 8) and CRZg are both closed so that the potentials at the anodes of the left and right-hand sections of tube V4 are direct-coupled to the control grid of tubes V5 and V6, respectively. Assuming that the head is not in its uppermost position (FIG. l) so that limit switch LS1 is not open, the plate circuit of tube V5 is completed from the left-hand terminal of the secondary transformer winding T281, resistor R16, the anode-to-cathode path of tube V5, limit switch LSI, contact CR'b, and through the second automatic head motor field winding AHMFBto the center tap of transformer secondary T281. Similarly, assuming that the automatic head (FIG. l) is not in its lowermost position so that limit switch LSZ is open, keeping relay CRS (FIG. 3) cle-energized and its contacts CRSC (FIG. 8) closed, the plate circuit of tube V6 is similarly completed from the right-hand end of the transformer secondary windings TESI, resistor RIF, the anode-tocathode path of tube V6, contacts CRSC and CR6C and through the eld winding AI-IMFB to the center tap of the secondary winding TZSI.

The automatic head motor is an induction motor with two separately excited field windings, windings AHMFA (FIG. 3)l and AHMFB (FIG. 8). By virtue of the capacitor CI?. in series with the winding AIPIMFA and the absence of such an impedance in winding AHMFB, the

currents in these two field windings are permanently 99 out of phase with one another. Tubes VS and V6 rectify the voltage applied thereto and hence pass alternate half cycles, so that the current through winding AI-IMFB, resulting from conduction by tube VS, is 180 out of phase with the current therethrough resulting from conduction by tube V6. Hence, while the current through the automatic head motor field winding AI-IMFB will be permanently out of phase with the current through the other winding, whether the effective current `through winding AHI/IFB leads or lags the current through the winding of current AHMFA is determined by the relative conductivities of tubes V5 and Vo which, through the before-described concatenations, is determined by the relationship between the actual arc voltage and the preselected arc voltage. Therefore, the automatic head motor will stand fast, or turn in one or the other of two directions, depending upon these voltage relationships.

Prior to the initiation of the arc, the voltage between the electrode EL (FIG. 7) and the work Wis much higher than the preselected are voltage. This voltage imbalance will cause the circuits of FIG. 8 and the bottom portions of FIG. 7 to drive the electrode EL (FIG. l) downwardly toward the work W. Assuming high frequency starting is employed, as described, at some point prior to the time at which the electrode strikes the work, the are will be formed. This will result in immediate reduction ofthe arc voltage relative to the selected arc Voltage and the automatic head motor will be correspondingly controlled to adjust the two voltages to equality.

Since the selected arc voltage is lower than the hold value of relay CRS (FIG. 7), that relay releases. Relay CRS, in releasing, opens its contact CRSb (FIG. 2) to terminate the operation of the spark-gap oscillator SGO (FIG. 7) and to release relay CIM (FIG. 2). Relay CIM, in releasing, closes its contact CPA-b (FIG. 8) to bypass resistor RX thereby to shift the voltmeter V to a more sensitive scale so that voltmeter V may, before the arc is struck, read the relatively high electrode-to-work voltage, and yet may read the substantially lower voltages after the arc is struck on a full-scale basis. Relay CRS (FIG. 7), in releasing, also affects the operation of certain timers as will be described.

It will be appreciated that while both relays CR6 (FIG. 3) and CPJ are concurrently operated as in incident of the automatic operation of the device, their contacts are functionally located in the circuit of FIG. 8 so that if relay CR7 (MG. 3) is operated and relay Clio is not operated, the head motor will drive the welding electrode upwardly, while it relay CR() is operated and relay CR7 is also operated, the welding electrode is caused to descend. The former of these characteristics is employed in controlling the equipment when one limit position is reached and both of these characteristics are employed in the manual control of the apparatus prior to the automatic phases of operation. Thus, if the automatic head reaches its lower limit so as to close limit switch LS?. (FIGS. 1 and 3), relay CRS (FIG. 3) is operated to open its contacts CRScz to release relay Cite. As a consequence, the welding electrode is automatically moved upwardly. In the manual phases of control, prior to the operation of relay BCR (FIG. 2), the voltage between conductors ith? and i624 may be selectively applied across relay CR7 (FIG. 3) or relays CRS and CR7 by the automatic head control switch AHCS to cause the welding electrode to be moved upwardly or downwardly, respectively. It will be further noted that if either during the manual or automatic phases of operation the head reaches its upper limit so as to open limit switch LS1 (FIGS. 1 and 8), the plate circuit of tube V is interrupted so that the motor will not be overdriven and so that travel will terminate.

Weld Current Control When contacts WPCa (FIG. 7) are closed as previously described, the three-phase alternating voltage appearing between conductors Ll, L2 and L3 is applied across a delta connected transformer array. Thus, the A voltage phase appearing between conductors Ll and L2 is applied across the serially interconnected transformer primary windings 31T? and VITP, the B phase appearing between conductors LZ and L3 is applied across the serially interconnected transformer primary windings 32TP and iSTP, and the C phase appearing between conductors L3 and L1 is connected across the serially interconnected transformer primary windings 33TP and MTP. The windings MTP to SSTP, with their respective, deltaconnected secondaries S, to 33TS, are the energy transferring devices for the welding operation. Each of the secondary windings SlTS to lTS is, however, serially interconnected with a controlling or regulating transformer primary winding 34HJ to 36T?, respectively, which function in a manner hereinafter to be described.

The regulated-amplitude output current of all three phases is rectiiied by a dry-disc rectifier array llRE, is

ltered by means including choke X4 and appears as an are current (assuming the arc has been struck) between the electrode EL and the work W.

As was noted in the introductory portion of this speciiication, the value of the current between the welding electrode EL and the work W may vary even though means are provided for maintaining a constant (or relatively constant) arc voltage. The preferred and disclosed means for maintaining a constant welding current, or a welding current which varies in a predetermined and preselected manner, is shown in FTGS. 5 to 7 of the drawmgs.

rTransformer primary windings lTP, lTP and 19T?, connected as described, serve as the means for sensing the amplitude of the primary-winding current in each of the phase branches, primary winding UTP in effect sensing the amplitude of the current through the A-phase primary winding SiTlP, primary winding lSTP in etiect sensing the amplitude of the current through the B-phase primary winding 32T?, and winding @TP in effect sensing the amplitude of the primary current through the C-phase primary winding SSTP. Consequently, there is produced in each of the respective secondary windings (FlG. 6) ilTS, ltiTS and 19T S, a voltage which is proportional to l2 the amplitude of the current in the primary windings 31T? (FIG. 7), SZTP and 33T?, repectively, these voltages being applied across individual loading resistors 451i, dell! and 47K, respectively.

In this specification, the terms primary and "secondary as applied to transformers are employed in their functional sense rather than in their design sense. Thus, for example, a step-down filament transformer having a design primary for connection to the line and a design secondary for connection to filaments may be and herein is employed reversely as a step-up transformer, and hence its design primary is a functional secondary and will be labeled a secondary, and conversely.

The output current from secondary winding l'TS (FIG. 6) is rectified by dri-disc rectiiers lf-SRE to MRE, the output current from secondary winding iSTS is rectitied by rectiiiers ESRB to ZiRE, and the output current from secondary MTS is rectiied by rectiiiers MRE, URE, NRE and MRE, producing a direct voltage across the load comprising the resistive portion of potentiometer 3P. The portion of this voltage appearing between the left-hand end of the resistive portion and the movable element of potentiometer i3? is applied across capacitor lC for a purpose hereinafter to be noted. lt will be observed that the elements JdR-Sill and MCL MC2, llCl and iZCZ serve as a lter.

Tube 12V serves to compare a fixed-amplitude direct voltage with a voltage having as one o1 its components the signal voltage appearing across capacitor l'7C and as another of its components the voltage appearing across capacitor ltC. The voltage across capacitor ieC is preferably selectable both as to a plurality of steady-state values and as to the rate of transition between steady-state values. Potentiometers 7l), QP and lill), variable resistors 8P and lll?, and relay contacts lllCRa, ltlCRb, lCRb and lCRc cooperatively control the portion of a tired voltage which is applied across capacitor MC and the rate at which that voltage across capacitor lC is caused to change.

The fixed-voltage source consists of elements represented primarily in FG. 5 of the drawings. The voltage appearing across secondary Winding MTSl is rectied by full-wave rectifier lltlV and applied across capacitor 13C. This voltage is iiltered by means including resistor 13R and capacitor MC, with the voltage appearing across the latter, and hence between conductors 17@ and 172, constituting the B voltage for tube lZV (FIG. 6). Thus, the two cathodes of tube 12V are connected through self-biasing resistor llR to conductor 17), and the two anodes of tube 12V are connected through individual load resistors 18K and 19K and through the balancing potentiometer Ml to conductor 172.

The voltage between conductors l'il and T72 is also applied across the serially interconnected resistor 14R (FIG. 5) and voltage regulating diode MV, and the resultant constant direct voltage across diode 11V is applied across the serially interconnected resistor lR and capacitor lSC, to produce a voltage between conductors i7@ and 174i, with the latter being positive relative to the former. The voltage on conductor 174 is applied through resistor 16E (FlG. 6) to the control grid of the left-hand section of tube 12V, producing a iow of current in the plate circuit of the left-hand section of tube 12V and a voltage drop across load resistor idR. While this current and voltage drop appears to be constant from the circuit elements thus far described, an additional signal is applied to this section of tube 12V so that the current through the tube and the voltage across load resistor TSR will vary, as will be seen.

The voltage between conductors F.7d and 174 is also applied, in parallel, across the resistive portions of potentiometers 7F, 9i) and itil). Potentiometer 'l (assuming it to be eflective, as will be described) controls the initial current and hence, the initial heat, potentiometer P controls the running current, and hence atrasos 13 the running heat, and potentiometer 1M controls the linal current, and hence the linal heat.

If itis desired to disable the control capabilities of the initial heat potentiometer QP, and start at a current and heat determined by the setting of potentiometer 7l), the up slope" switch GSW (FlG, 2) is moved into engage ment with its lower contact whereupon relay lltlCR will be operated assoon as the control-on switch lPB is operated to operate relay ACR to close its contacts ACRa. However, it will be assumed that it is desired to take full advantage of the capabilities of the system so that the 11p-slope switch 6SW is in its uppermost position as shown.

In that case, at the time the arc is iirst struck, relay lliiCR, as well as relay 13CR, is still released. As a result, contacts ltlCRa (FIG. 6) and lCRb are closed, while contacts itlCRb and ISCRC are open. Hence, at this time the voltage appearing between the moving element (in its preselected position) of potentiometer ,)P and conductor 17@ is applied across capacitor 16C. In one mode of operation of the system, after the arc is struck and the arc voltage is reduced to a value to cause the release of relay CRS (FIG. 7), a circuit is completed from the Conductor lltlZ (FIG. 2), through the now-closed contact CRlia, through the now-closed contact CRSQ, through switch USD (assumed to be closed to its No. 1 Contact), through the up-slope switch 65W, and through the winding of relay lltlCR to conductor 104 whereby relay tlCR is operated.

The resultant opening of contact lilCRa (FG. 6') relieves potentiometer @P of control over the voltage across capacitor 16C. The closure of contact itlCRb causes the voltage between the movable element of potentiometer 7i) and conductor 17@ to be applied across a circuit including variable resistor SP and capacitor 16C. Assuming, as is normally the case, that the setting of potentiometer "iP is different from that of potentiometer 9F, the voltage across capacitor 16C must change, the rate oi this change being established, in part, 'oy the setting of variable resistor 8P, whereby the up slope time is determined. Capacitor 16C then discharges to a value established by potentiometer '7P.

In an alternative mode of operation of the system, the up-slope Idelay switch USD (FlG. 2) is closed to its No. 2 contact. Consequently, the clos-ure of contacts CRSa will not produce the immediate operation of relay MCR,

but will energize start lead SLab to energize the weld travel delay timer TDA (FIG. 3). At Vthe expiration of the set delay interval, contact ZCRAb is closed to `complete a circuit from energized conductor litio, now-closed contacts TDZa and 2CRAb, conductor 129, No. 2 contact and swinger `of switch USD (FIG. 2), upper contact and swinger of switch GSW and the winding of relay 10CR. Hence, the weld current is maintained at the initial-heat level for a preselected interval to permit the building of a `selected molten pool. lIt it is desired that the delay between the release of relay CRS and the operation of relay 10'CR be controllable independently of the weld travel delay interval, a separate timing unit may be provided. Thus, as a speciiic example, an additional timer such as that represented in HG. ll of the drawings may be connected between conductors 102 and 101i, vvith its start lead SL connected to start lead SLczb (FIG. 3). Switch USD (iFIG. 2) may be eliminated and the conductor between its moving element and the upper contact of switch @SW may be omitted. The upper contact of switch y6SW may then be connected to conductor 166 through a normally open time-delay contact, of the added timer unit, ie., through a normally open contact of the relay 2CR (FIG. 1l) in that added timer.

Potentiometer 7P continues to control the amplitude of thewelding current untila time somewhat after that at which limit switch LS4.('FiGS.-1 and 4), as an example, is tripped to closed position to initiate the current decay operation. When limit switch L84 (FG. 4) is closed,

the current decay delay unit rFDC is energized over a circuit from conductor 102 (FIG. 2), contacts ACRa and BCRb, conductor 120, limit switch LS4 (FIG. 4), and the start lead SLc. Unit TDC seals in, and, after the preset time interval, closes its contacts ZCRCa to energize the tailing time delay unit T-DE, which seals in. At the instant of energization of unit TDE, its Contact lCREb (FIG. 2) closes to operate relay 13CR, assuming that switch 78W is closed.

Relay 13CR, in operating, opens its contact 13CRb (FIG. `6) to relieve potentiometer 7l of control over the voltage across capacitor 16C, and closes its contact 13CRc so that the voltage .appearing between the movable element of the final-heat potentiometer 10P and conductor is applied across variable resistor 11P and capacitor 16C. Capacitor 16C will charge to a new value, set by potentiometer 10P, at a rate determined by the setting of they down-slope-control variable resistor v1-1P.

It will be observed that the linal heat potentiometer 10P and the down-slope time variable resistor 11F may be disabled to perform their functions by opening switch 'SW (FIG. 2) in the energizing circuit of relay 13CR, in which case the lfinal heat will remain the same as the run heat, as established by potentiometer 7l?.

The sum of the voltages across capacitors 16C and 17C is applied as a signal to the input circuit of the right-hand sect-ion of tube 12V. Thus, the input circuit of that section may be traced `from the grid thereof, current limiting resistor ZR, capacitor 17C, capacitor 16C, and resistor 17R to the cathode of that section. Therefore, the input signal to the right-hand section of tube 12V includes 'one component, the voltage across capacitor 17C, which is varying in amplitude .as a function of the current in the primary windings of the welding transformer, and another component, the voltage across capacitor 16C, which is iixed or varying in a preselected manner and in accordance with the status yof the welding operation.

This composite input signal produces 4a resultant variation in the current iiow in the plate circuit of the righthand section of tube 12V and a consequent variation in the anode potential thereof, due to the voltage drop across load resistor l19R, which is applied as an output signal to conductor 176. As the current in the primary windings of the welding transformer increases, as an example, the voltage across capacitor 17C increases to produce an increased plate current in the right-hand section of tube 12V and a consequent reduction in the amplitude of the output voltage on conductor 1:76, and a similar result obtains if the voltage across capacitor 16C increases. This change in the amplitude of the plate current in the righthand section of tube 12V will produce a corresponding change (increase) in the voltage drop across bias resistor 17R and will thereby change (increase) the voltage of the cathode of the left-hand section of tube 12V, producing a change in the bias of that section and a consequent change (increase) in the output voltagey signal applied to conductor 178. It Iwill be observed that the direction of the change of voltage on conductor 176 is opposite to the direction of change of voltage on conductor 178. Thus, this cathodecoupling serves to emphasize the signal changes, so that a given change in the amplitude of the input signal will produce a greatly magnified change of th-e potential difference between conductors 176 and 173.

The output signal voltage appearing between conductors 176 and 17S is modified by the addition of a fixed, positive biasing potential to thepotential on conductor 178. Thus, the line voltage appearing across the secondary winding 14TS3 (FIG. 5) is rectified by dry disc rectifiers MRE and 15RE and applied across capacitor ISC (FIG. 6) as well as across the serially interconnected resistor SSR and voltage regulating diode 13V, and the resultant constant direct voltage across tube 13V is applied across the resistive portion of potentiometer'12P. A selected portion of this total available voltage is applied across antenne capacitor 19C which is connected between conductors 173 and ldd. Hence, even under conditions of exact yequilibrium of the two sections of tube 12V wherein the voltage difference between conductor 176 and 17S is zero, conductor 13) is positive relative to conductor 176 by an amount equal to the voltage across capacitor 19C.

The potential difference existing between conductors 1S@ and 176 is employed to control the conductivity and hence the effective resistance offered by, the dual triodes 7V, 8V and 9V. Each pair of control grids of each of these tubes is connected through an individual current limiting resistor SSR, 3eR and 37K to conductor 11.76, and all of the cathodes of these three tubes are connected to conductor ldd. It will be observed that even when the output of the two sections of tube MV is balanced, each of the tubes 7V to 9V is biased negatively by an amount equal to the voltage across capacitor 19C.

Each of the individual circuits including tubes 7V, 3V and 9V, respectively, is individual to one of the three power-supply phases A, B and C, respectively, and serves to produce an output signal which is shifted in phase relative to the particular power-supply phase with which it is associated, the amount of that phase shift varying as a function of the amplitude of the direct-voltage signal applied to the individual tubes input circuit.

Referring to FIG. 5 of the drawings, power-supply phase A appearing between conductors Ll and L2 is applied across the transformer primary winding STP, phase B appearing between conductors L2 and L3 is applied across the transformer primary winding 9TP, and phase C appearing between line conductors L3 and Ll is applied across the primary transformer winding MTP. The associated secondary windings (FlG. 6) STS, @TS and NTS are operatively associated with tubes 7V, 8V and 9V, respectively.

Considering the circuit including tube 7V, the A- phase alternating voltage appearing across the secondary winding STS is, in effect, applied across a serially interconnected reactance and resistance, with the output being taken between the point of junction of the reactance and resistance and the center tap of the transformer winding STS. Capacitor 7C serves as the reactive element and is connected to the right-hand terminal of the secondary winding STS. The dual-section tube 7V, dry disc rectiers SRE and SRE, and variable resistor 4P compositely serve as the resistive element, which is variable in magnitude to produce a selected degree of phase shift. The output signal is derived from the primary transformer winding MTP which is connected between the center tap of winding STS and the point of junction of the capacitor '7C and the resistive network. During one half cycle of the applied voltage across transformer secondary STS (that half cycle during which the right-hand terminal of secondary STS is positive relative to the left-hand terminal) the resistive path includes the anode and cathode of the right-hand section of tube 7V, rectifier SRE, and variable resistor 4P. During the other half cycle of the Voltage across transformer secondary STS, the resistive path includes variable resistor 4P, the anode and cathode of the left-hand section of tube 7V and rectifier 9RE.

As is well known, the amount of phase shift may be varied by varying the magnitude of the resistive component, and the magnitude of this resistive component may, in effect, be varied by changing the direct voltage applied to the input circuits of the two sections of tube 7V. If the input signal to tube 7V is such as to render the grids sufficiently negative relative to the cathodes to render the tube effectively non-conductive, the resistance offered is very high and the phase shift is maximum. With the parameters employed in a practical embodiment of the invention, this maximum phase shift may amount to about 135. As the negative bias on tube 7V is reduced, its effective resistance is correspondingly reduced, so that as tube 7V approaches saturation, the angle of phase shift approaches zero degrees,

Therefore, an increase in current in the power transformer windings (FlG. 7) 31T?, SZTP and SSTP will cause the grids of tube 7V (and of the corresponding tubes in th other phase shifting circuits) to become more negative relative to their cathodes, increasing the phase shift. Conversely, a decrease in the amplitude of the sensed signal will cause the control grids of tube 7V to become less negative relative to their cathodes and the amount of phase shift will be reduced.

The phase shifting circuit including tube 8V, individual to voltage phase B, and the circuit including tube 9V, individual to phase C, function identically to that of the phase A circuit described. The operation of these three circuits may be precisely balanced by adjusting the position of the variable resistors fil), SP and 6P.

The output signal from each of these phase shifting circuits is employed to control the tiring angle of a pair of thyratrons individual to each of the phase-shift circuits and individual to each of the voltage phases. Thus, thyratrons liv' and ZV (FIG. 7) are individual to voltage phase A and individual to the phase A shifter including tube 7V, thyratrons 3V and 4V are individual to voltage phase B and to the B phase shifter including tube 8V, and thyratrons 55V and 6V are individual to voltage phase C and to the C phase shifter including tube 9V.

Considering the A-phase thyratron circuit, energy is supplied to the thyratrons lV and 2V through the secondary transformer winding 15d-TS, the primary winding MTP of which is serially included with the A-phase power secondary winding SETS, as before noted. Hence, a voltage is applied to the anodes of thyratrons lV and 2V which corresponds to the voltage phase A. Since each of the thyratrons lV and 2V is connected across the winding MTS, the average current amplitude through winding .Qi-@TS may be controlled by controlling the firing angle of those thyratrons, and the firing angle can in turn be controlled by varying the phase relationships between the grid and anode voltages.

Thus, an input signal is applied to the secondary transformer windings llTSl and llTSZ via transformer primary IllTP (FiG. 6). lt is assumed, as an example, that these alternating voltages at the transformer secondaries lag the respective alternating plate voltages by an angle approaching zero degrees as a minimum and as a maximum. The voltage appearing across the secondary winding lllTSt is applied between the grid and cathode of thyratron 1V through a network including rectifier ZRE, resistors lR and 2R and capacitor 1C, and the voltage appearing across the secondary winding 11TS2 is applied between the control grid and cathode of thyratron 2V through a network including rectifier SRE, resistors 3R and 4R, and capacitor 2C. The function of rectiiiers ERE and SRE is merely to insure that the control grids will not be driven positive at a time when the respective anodes are negative.

The arnplitude of the average current in the transformer secondary winding iiTS controls the amplitude of the average current through the corresponding primary wind- '.rg 34T?, and thereby controls the average current through the power secondary winding SSlTS. Otherwise stated, the tiring angle of thyratrons lV and 2V controls the reactance of the transformer primary winding 34T? and hence the impedance offered by that primary winding to the flow of current through the power secondary winding SlTS.

Reviewing the entire concatenation, and considering, as an example, a change in one direction of the current in but one of the phases, an increase in the welding arc circuit current represents an increase in the alternating current in the A-phase power secondary winding 3llTS, which produces au increase in the current in the A-phase primary transformer winding SilTP. As a consequence, there will be an increase in the current in the A-phase signalsensing transformer primary winding iTP, resulting in an increased current through the secondary winding 17TS 

1. IN A WELDING APPARATUS FOR WELDING A WORKPIECE AND HAVING A WELDING ELECTRODE AND MEANS FOR MOVING THE ELECTRODE ALONG THE WORKPIECE, THE COMBINATION OF ELECTRODE POSITION DETECTING MEANS OPERABLE WHEN THE ELECTRODE HAS MOVED TO A PRESELECTED POSITION ALONG THE WORK, AN ELECTRON-DISCHARGE DEVICE HAVING AN INPUT CIRCUIT, A CAPACITOR SERIALLY INCLUDED IN SAID INPUT CIRCUIT, A FIRST VOLTAGE SOURCE, MEANS EFFECTIVE WHEN WELDING COMMENCES TO CONNECT SAID FIRST SOURCE ACROSS SAID CAPACITOR, A SECOND VOLTAGE SOURCE, A RESISTOR, AND MEANS CONTROLLED BY SAID DETECTING MEANS FOR CONNECTING SAID SECOND VOLTAGE SOURCE AND SAID RESISTOR ACROSS SAID CAPACITOR. 